Instructor's use of humor in college classrooms is generally viewed positively by students and has been correlated with positive student learning, motivation, perceptions of instructor immediacy, and classroom environment. However, the majority of studies on instructor humor used in college classrooms have explored student perception of funny humor and not of unfunny or offensive humor. Female students, who are more likely to report feeling unwelcome in college science courses, may be particularly affected by instructor use of unfunny or offensive humor. However, few studies have explored how male and female students perceive instructor humor and more specifically, whether male and female students perceive different subjects as offensive. Further, no humor study has been conducted in the context of college science courses.This study was conducted as a course‐based undergraduate research experience (CURE) in biology education with 12 undergraduate and 4 graduate students. Students in the CURE engaged in the process of selecting a research question, iteratively developing a survey tool, collecting data, and analyzing data. We surveyed 1637 undergraduate students across 25 different college science courses at one institution and found that 97% of students appreciate when instructors use humor in college science classes. Using a combination of grounded theory and content analysis, we identified 12 distinct reasons for why students appreciate instructor use of humor in science classes, including that it enhances student learning, makes students more excited to attend class, and makes the instructor more approachable. We found that instructor use of funny humor positively impacted student sense‐of‐belonging to the science classroom, instructor relatability, and student attention to course content. We also found that while instructor use of unfunny humor appeared to neither have a positive nor a negative effect on students, instructor use of offensive humor negatively impacted student sense‐of‐belonging to the science classroom and instructor relatability. There was no difference in the extent to which instructor use of humor positively or negatively affected male and female students. Lastly, we identified a suite of subjects that students broadly perceive as funny, yet less than 5% of students perceive as offensive. We also identified a suite of subjects that some students perceive as funny, yet more than 50% of students perceive as offensive. Specifically, female students were more likely to be offended by humor used by instructors. We hope that these findings will aid in the development of more inclusive classrooms by encouraging instructors to use humor that is most likely to benefit all students.Support or Funding InformationNoneThis abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.